Jus soli and jus sanguinis
The two basic rules for acquiring citizenship at birth: jus soli (right of the soil) grants it to those born on the territory; jus sanguinis (right of blood) grants it to children of citizens wherever they are born.
In more detail
Most states combine the two. Unconditional jus soli is common in the Americas, including the United States and Canada. Many European states use jus sanguinis with conditional jus soli: since 2024 Germany grants citizenship to children born there if a parent has lived lawfully in Germany for five years with permanent residence. Rogers Brubaker linked France's territorial tradition and Germany's descent-based tradition to different ideas of nationhood. Mismatches between the two rules can leave children stateless or with several nationalities. Naturalisation, the third route, depends on residence, language and integration conditions.